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Azimuthal anisotropy and correlations at large transverse momenta in p+p and Au+Au collisions at sqrt[sNN] = 200 GeV (2004)

J. Adams Jens Berger Thomas Dietel Thorsten Kollegger Jens Sören Lange Reinhard Stock et al. STAR Collaboration

Results on high transverse momentum charged particle emission with respect to the reaction plane are presented for Au+Au collisions at sqrt[sNN]=200 GeV. Two- and four-particle correlations results are presented as well as a comparison of azimuthal correlations in Au+Au collisions to those in p+p at the same energy. The elliptic anisotropy v2 is found to reach its maximum at pt~3 GeV/c, then decrease slowly and remain significant up to pt ~ 7-10 GeV/c. Stronger suppression is found in the back-to-back high-pt particle correlations for particles emitted out of plane compared to those emitted in plane. The centrality dependence of v2 at intermediate pt is compared to simple models based on jet quenching.

Azimuthal anisotropy and correlations in the hard scattering regime at RHIC (2003)

Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

Azimuthal anisotropy (v2) and two-particle angular correlations of high pT charged hadrons have been measured in Au+Au collisions at sqrt[sNN]=130 GeV for transverse momenta up to 6 GeV/c, where hard processes are expected to contribute significantly. The two-particle angular correlations exhibit elliptic flow and a structure suggestive of fragmentation of high pT partons. The monotonic rise of v2(pT) for pT<2 GeV/c is consistent with collective hydrodynamical flow calculations. At pT>3 GeV/c, a saturation of v2 is observed which persists up to pT=6 GeV/c.

Azimuthal anisotropy at the Relativistic Heavy Ion Collider: the first and fourth harmonics (2004)

J. Adams Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We report the first observations of the first harmonic (directed flow, v1) and the fourth harmonic (v4), in the azimuthal distribution of particles with respect to the reaction plane in Au+Au collisions at the BNL Relativistic Heavy Ion Collider (RHIC). Both measurements were done taking advantage of the large elliptic flow (v2) generated at RHIC. From the correlation of v2 with v1 it is determined that v2 is positive, or in-plane. The integrated v4 is about a factor of 10 smaller than v2. For the sixth (v6) and eighth (v8) harmonics upper limits on the magnitudes are reported.

Azimuthal anisotropy in Au+Au collisions at SNN=200GeV (2005)

J. Adams Jens Berger Thomas Dietel Thorsten Kollegger Jens Sören Lange Reinhard Stock et al. STAR Collaboration

The results from the STAR Collaboration on directed flow (v1), elliptic flow (v2), and the fourth harmonic (v4) in the anisotropic azimuthal distribution of particles from Au+Au collisions at sqrt[sNN]=200GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a blast-wave model. Different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v2, scaling with the number of constituent quarks and parton coalescence are discussed. For v4, scaling with v22 and quark coalescence are discussed.

Azimuthal anisotropy of K0S and Lambda + Lambda -bar production at midrapidity from Au+Au collisions at sqrt[sNN]=130 GeV (2002)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We report STAR results on the azimuthal anisotropy parameter v2 for strange particles K0S, Lambda , and Lambda -bar at midrapidity in Au+Au collisions at sqrt[sNN]=130 GeV at the Relativistic Heavy Ion Collider. The value of v2 as a function of transverse momentum, pt, of the produced particle and collision centrality is presented for both particles up to pt~3.0 GeV/c. A strong pt dependence in v2 is observed up to 2.0 GeV/c. The v2 measurement is compared with hydrodynamic model calculations. The physics implications of the pt integrated v2 magnitude as a function of particle mass are also discussed.

Azimuthally sensitive Hanbury Brown-Twiss interferometry in Au+Au collisions at sqrt[sNN]=200 GeV (2004)

J. Adams Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

We present the results of a systematic study of the shape of the pion distribution in coordinate space at freeze-out in Au+Au collisions at BNL RHIC using two-pion Hanbury Brown-Twiss (HBT) interferometry. Oscillations of the extracted HBT radii versus emission angle indicate sources elongated perpendicular to the reaction plane. The results indicate that the pressure and expansion time of the collision system are not sufficient to completely quench its initial shape.

Centrality Dependence of High-pT Hadron Suppression in Au+Au Collisions at sqrt[sNN]=130 GeV (2002)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

Inclusive transverse momentum distributions of charged hadrons within 0.2<pT<6.0 GeV/c have been measured over a broad range of centrality for Au+Au collisions at sqrt[sNN]=130 GeV. Hadron yields are suppressed at high pT in central collisions relative to peripheral collisions and to a nucleon-nucleon reference scaled for collision geometry. Peripheral collisions are not suppressed relative to the nucleon-nucleon reference. The suppression varies continuously at intermediate centralities. The results indicate significant nuclear medium effects on high-pT hadron production in heavy-ion collisions at high energy.

Coherent rho 0 production in ultraperipheral heavy-ion collisions (2002)

Clemens Adler Z. Ahammed C. Allgower Jens Berger Thomas Dietel Dominik Bernhard Flierl Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

The STAR Collaboration reports the first observation of exclusive rho 0 photoproduction, AuAu-->AuAu rho 0, and rho 0 production accompanied by mutual nuclear Coulomb excitation, AuAu-->Au [star] Au [star] rho 0, in ultraperipheral heavy-ion collisions. The rho 0 have low transverse momenta, consistent with coherent coupling to both nuclei. The cross sections at sqrt[sNN]=130 GeV agree with theoretical predictions treating rho 0 production and Coulomb excitation as independent processes.

Cross sections and transverse single-spin asymmetries in forward neutral-pion production from proton collisions at sqrt[s] = 200 GeV (2004)

J. Adams Clemens Adler Jens Berger Thomas Dietel Dominik Bernhard Flierl Thorsten Kollegger Jens Sören Lange Reinhard Stock Christof Struck et al. STAR Collaboration

Measurements of the production of forward high-energy pi 0 mesons from transversely polarized proton collisions at sqrt[s]=200 GeV are reported. The cross section is generally consistent with next-to-leading order perturbative QCD calculations. The analyzing power is small at xF below about 0.3, and becomes positive and large at higher xF, similar to the trend in data at sqrt[s] <= 20 GeV. The analyzing power is in qualitative agreement with perturbative QCD model expectations. This is the first significant spin result seen for particles produced with pT>1 GeV/c at a polarized proton collider.

d-bar and 3He-bar Production in sqrt[sNN] = 130 GeV Au+Au Collisions (2001)

Clemens Adler Z. Ahammed C. Allgower et al. STAR Collaboration Reinhard Stock

The first measurements of light antinucleus production in Au+Au collisions at the Relativistic Heavy-Ion Collider are reported. The observed production rates for d-bar and 3He-bar are much larger than in lower energy nucleus-nucleus collisions. A coalescence model analysis of the yields indicates that there is little or no increase in the antinucleon freeze-out volume compared to collisions at CERN SPS energy. These analyses also indicate that the 3He-bar freeze-out volume is smaller than the d-bar freeze-out volume.

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